1. Field of the Invention
The present invention relates generally to a method and apparatus for controlling the performance of an internal combustion engine. More specifically, the present invention relates to a technique for calibrating components used to control a fuel injection system of in internal combustion engine to enhance consistency and predictability in the performance of the engine.
2. Description of the Related Art
Internal combustion engines are used to provide mechanical power in a number of applications. Some of the more recognized uses include automobiles, motorcycles, watercraft, and so forth. Other uses range from small engine applications such as lawn mowers to large scale applications including industrial machinery. An internal combustion engine operates by igniting a mixture of air and combustible fuel within one or more combustion chambers to provide rotational motive force, or torque, to do work. For example, in an automobile, the engine provides torque to the wheels to impart a driving force to the vehicle. Likewise, when used in a watercraft, the engine is typically coupled to a prop which, when rotated, provides a thrust to the watercraft.
Engine performance is greatly dependent upon proper fuel delivery to the combustion chamber. For example, the torque produced by an engine is generally proportional to the volume of fuel introduced into the combustion chamber for a given combustion cycle. Engine speed, on the other hand, is generally a function of the flow rate of fuel to the combustion chamber. Under typical operating conditions, accurate and predictable control of both torque and engine speed is desired. Thus, the fuel delivery system is an integral and extremely important component in engine performance.
There are many methods of providing fuel to a combustion chamber in an internal combustion engine. One of the more widely utilized methods is fuel injection. While discussed in broad terms here, fuel injection may also be broken down into numerous techniques and methods. Typically, fuel injection involves employing one or more pumps to provide a source of pressurized fuel. A fluid actuator, such as a solenoid operated valve, initiates a flow of pressurized fuel to an injection nozzle. In other systems the fluid actuators produce a surge in fuel pressure. The surge in pressure then causes the injection nozzle to open, allowing pressurized fuel to flow through the injection nozzle into the combustion chamber. Some types of injection systems may integrate the pump and injection nozzle into a single unit. In such a case, the pump is electrically operated and controlled to deliver desired volumes of pressurized fuel at desired rates.
Regardless of the type of injection being used, proper timing and control of the injection event becomes critical. Improper fuel volumes, rates of delivery, cycle times, or timing of the injection with the spark ignition in the combustion can all lead to poor engine performance. Typically, a programmable logic device, or an electronic control unit, controls the operation of the fuel injection system. Through appropriate circuitry, the programmable logic device generates signals to be sent to the fluid actuators or pumps, depending on the system type. These signals control the operation of the fluid actuators or pumps to deliver the right amount of fuel through the nozzle at the appropriate time.
In modern fuel injection systems, numerous factors may contribute to inconsistent and unpredictable performance of a fuel delivery system. Stacking of tolerances in the mechanical components may serve to create unpredicted performance of the pump, fluid actuator, or nozzle assemblies. Likewise, stiction within any of the above mentioned components may lead to unpredictability and inefficiency. Furthermore, in most cases, an engine requires multiple injection devices and associated actuators or pumps, typically one for each combustion chamber. In such instances, variances in the injection control components or circuitry from one combustion chamber (or control channel) to another complicates the matter even further. Variances in the controller continue to add to the unpredictability. For example, the controller often employs channels for the control of the injection devices. Each device is controlled by its own individual channel. Because of tolerances in the components used in each channel""s circuitry, there may be slight variances in signals produced from channel-to-channel. Such variations, although small, may significantly affect engine performance, particularly at lower per cycle injection rates. Moreover, such variations may also result in higher exhaust emissions, which in most cases are preferably kept to a minimum.
There is, therefore, a need in the art for the ability to improve fuel injection systems such that fuel delivery is consistent and predictable. These improvements should not only be in terms of cyclic performance (i.e. between cycles), but also from one channel to another channelxe2x80x94or from one combustion chamber to another combustion chamberxe2x80x94within a given internal combustion engine (i.e. within each cycle).
The present invention is directed to overcoming, or at least reducing the affects of, one or more of the problems set forth above. The technique offers a simple and straightforward way to compensate for part-to-part differences, to provide significantly improved engine performance, excellent predictability in operation, and reduced emissions.
The technique provides a method of calibrating an electronic control unit for an internal combustion engine. The electronic control unit may have multiple channels with each channel being adapted to provide an input drive signal to a fuel delivery apparatus. In accordance with one aspect of the technique, a first channel is selected for calibration. A reference signal of desired and known parameters is defined such that it is indicative of the desired performance of a fuel delivery apparatus such as a fuel injection device. A command signal is generated and applied to the selected channel. The channel circuitry then generates a drive signal in response to the command signal. A desired parameter of the drive signal is measured for comparison with the known parameter of the reference signal. If necessary, the command signal is then adjusted so as to produce a modified drive signal which has a parameter with reduced variation from the known reference parameter.
The process of adjusting the command signal may be accomplished by changing the duration of the command signal by a predetermined increment of time. The process may then become iterative until the modified drive signal has a parameter which comes within an acceptable range when compared to the known reference parameter. The total adjustment to the command signal is then stored into a memory device for subsequent recall. Having calibrated the selected channel, another channel may be selected and the process repeated until all channels of the electronic control unit are calibrated.
In accordance with another aspect of the invention, an electronic control unit is provided for control of a fuel delivery system on an internal combustion engine. The electronic control unit includes a microprocessor with a memory storage device coupled to the microprocessor. A driver circuit is also coupled to the microprocessor. The driver circuit includes multiple channels with each channel providing a drive signal to a fuel delivery apparatus in response to a command signal from the microprocessor. The command signal is augmented by a customized parameter offset. The customized parameter offset assists to produce a drive signal with a predetermined characteristic.
In accordance with another aspect of the invention, an internal combustion engine is provided having an electronic control unit with the qualities and components of those described above herein.